Method of testing the flammable condition of a mixture of air or oxygen with a flammable gas or vapor



N. J. THOMPSON Y 1,779,569

E FLAMMABLE CONDIT WITH A F Oct. 28, 1930.

METHOD OF TESTING TH ION OF A MIXTURE LAMMABLE GAS OR VAPOR l4 1926 OF AIR OR OXYGEN 2 Sheets-Sheet 1 Filed Sept.

wllvmn llll- -Inv'enTor. Normand Thom pson Oct- 3 N. J. THOMPSON 1,779,569

METHOD OF TESTING THE FLAMMABLE CONDITION OF A MIXTURE OF AIR 0R OXYGEN WITH A FLAMMABLE GAS 0R VAPOR Filed Sept. 14, 1926 2 Sheets$heet 2 1/ l/II/I/lII/IIIIIIIIIIII lnv enTdr. Norman J. Thompson Patented Oct. 28, 1930 UNITED STATES- PATENT OFFICE Romain J. 'rnonrson; or WELLESLEY mLs,,.mssAcnusErrs IETHOD OI TESTING THEFLAMMAZBLE CGNDITIdN OI AHIXTUBE OF AIB 0B OXYGEN WITH A FLAMMABLE GAS OR VAPOR i Application filed September 14, 1926. Serial No. 135,822.

This invention relates to methods for continuously determining the flammable condi-' tion of a mixture of an and flammable gases,

such as are widely employed commercially in various arts in which flammable, volatiie solvents are used, in order that suitable steps may be taken to prevent the ixture from reaching or dangerously ap lower explosive limit.

The terms gas and gases are used herein to include not only such materials as are true gases at ordinary temperatures, but also vapors of materials which are normally liquid at ordinary temperatures.

This invention further relates to methods which may be utilized to determine the proportion of the flammable constituents of a mixture of flammable gases with air or oxygen irrespective of the particular gas or gases which may constitute the flammable constituents thereof.

The invention further comprises a method of automatically regulating the proportions of air or oxygen and flammable gases in a chamber in such a'manner as to avoid with certainty the production of explosive mixtures therein. I

Other objects and features of the invention will more fully appear from the following description and the'accompanying drawingsand will be particularly pointed out in the claims. .The present method and apparatus which may be employed in the performance thereof are particularly valuable in commercial arts in which volatile solvents are em 10 ed which are subsequently vaporized an thereof mixed .with air as in japanmng, enamelling, and various branches of the rubher industry and other industries.

Inasmuch as the volatile solvents used in commercial industries are largely hydrocarbons, the present method and apparatus will be more particularly described with.

reference thereto, although it will be understood, as will hereinafter more fully appear, that the' invention is also applicable to the testing of the flammable condition of mixtures of air or oxygen with other flammable roaching the t e vapors vapors and gases, such for example, ashydrm gen, carbon monoxide,-etc. Y

The term hydrocarbon isemployed herein in a broad sense to define any vaporor gaseous compounds of carbon and hydrogen, or of carbon, hydrogen and oxygen, or any mixture of such vapors or hydrocarbons either alone or combined with oxy en. Usually commercial hydrocarbons, such as'gasoline, naphtha, henzol, and the like, comprise mixtures of various compounds containing hydrogen and carbon and are all included, together with various other hydrogen, carbon and oxygen-containing mixtures, within the above definition of hydrocarbon. Such hydrocarbons, when mixed with air in proper proportions, form an explosive mixture and the present invention provides means for determining with exactness the proportion'of flammable vapors in the mixture of such hydrocarbons with air so that the approach of the content of flammable gases or vapors in a mixture with air to the lower explosive limit may be determined .and indicated in commercial apparatus and suflicient additional air or oxygen supplied to. prevent explosion under the heat conditions existing.

In drying and baking chambers, such as are employed in enamelling or japanning the surfaces of metals, and in the rubber industry,

the hydrocarbons which are used as solvents are rapidly volatilized so after the coated materi ls are placed in the oven and if the air introduced is insuflicient in quantity an explosive mixture is quickly formed. The mtroduction of air into such ovensis usually maintained'at a substantially constant rate and in numerous instances serious explosions have occurred by the overchargingof the ovens, or by the failure to introduce a sufficient amount of air to maintain the mixture in the oven below the lower explosive limit.

advised of the exact conditions in the various parts of the chamber and, therefore, will be able to take suitable steps to avoid explosion. In usual methods of testing the flammable condition of mixtures of vapor'and hydrocarbon a sample of vapor isvtaken from the oven, or other chamber, and is thereafter subjected to an analytical or other test to determine the proportion of hydrocarbon contained therein. Such tests are subject to considerable error by reason of the condensation of the hydrocarbon vapors. The present invention contemplates the testin of the mixture at a temperature in excess 0 that which will permit condensation.

I have found that the minimum temperature necessary to prevent condensation below explosive strength mixture i of the hyrogen an carbon-containing vapors, which are commercially employed at the present time, is usually not over 212 F. The present invention, therefore, contemplates where necessary, the maintenance of the mlxture at a temperature in excess of 212 F. or at such other temperature as is necessary to prevent con-' densation below flammable strength.

I have discovered that at any 'ven temperature and at the lower limit 0 explosive strength of mixtures of hydrocarbon vapors orgases with air, the heat of complete combustion of a definite volume of the mixture is approximately the same re ardless of the partlcular' hydrocarbon or hydrocarbons in question. It, therefore follows that at any definite fraction of the lower explosive limit strength different mixtures will give identical heat units-of combustion. Different hydrocarbons inmixture with air vary in the percentage of vapor required to produce complete combustion at the lower explosive or ammable limit, for example, the lower explosive limit percentage of gasoline is approximately 1.3%; of benzol- 1.4%; of

acetylene 2.5% and of, methane 5.5%. The heat of complete combustion per 100 cubic centimeters of vapor and air mixture at, for example, 20-degrees C. and 760-mm. baro metric pressure, for all of these, as well as of other hydrocarbon compounds, is .the same, being approximately fifty calories in each case.

The present invention is based upon the above discoveries.

I have also found that an instrument for performing the process herein described when calibrated for a particular hydrocarbon may .be employed to determine the proportion of flammable vapor or gases of any other hydrocarbon.

Furthermore, I have .found that the process and the apparatus for performing the same is not limited to hydrocarbons so that the same instrument may, by suitable caligas or gases, such ashydrogen or carbon monoxide.

The novel method of testing flammable or or explosive condition of a mixture of flammable gases and air may, in its broad sense, be defined as consisting in maintaining a continuously flowin sample of the mixture at a temperature su cient to prevent-condensation, causingcombustion of the flammable gases of said sample, and measuring the increase in temperature produced thereby and in determining from such increase in temperature the proportion of flammable vapors in the mixture.

In performing the method a current of hydrocarbon-containing air is caused to flow through a conduit in which it is maintained at a temperature in excess of the temperature of condensation of an explosive mixture of the flammable material and is subjected, while in the conduit, -to means, preferably a catalyst,-heated or not, or a heated inert material, which will cause combustion of the flammable content of the mixture. The increase in temperature caused by such c'ombustion is measured by suitable means and ,the proportion of flammable material, which is proportional to the increase in temperature caused by such combustion, is determined therefrom. A thermocouple, located in contact with the catalyst or inert material, or in the field of combustion in proximit thereto, provides a convenient means for eterminmg the proportion of the flammable material in the mixture as the rise in voltage in the thermocouple is proportional to the increase in temperature produced by such combustion and consequently to the proportion of flammable material contained in the mixture.

It will, however, be understood that various other means may be employed for determining the increase in temperature caused by such combustion and that the resent method contemplates the utilization 0? any means for accomplishing this urpose.

Different types 0 apparatus are disclosed in the accompanying drawings which are adapted to perform the method herein described, and it willbe understood, therefore, that the method in' its broad sense contemplates the employment of any apparatus or means for producing the various steps of the method herein described.

In the drawings:

Fig. 1 is a view, partly in section, of a preferred form of apparatus for testing the ammable condition of a mixture of 8.1!,01 oxy n with a flammable gas or va or in accor ance with the method herein escribed;

Fig. 2 is a detail sectional view on line 22 Fig. 1 of the flashback preventer;

ig. 3 is a detail elevation sh owing the heating unit for raising the tem erature of the mixture to a temperature s cient to cause combustion of the hydrocarbon or other flammable material contained in the mixture, illustrating also the catalyst or inert material in contact with or in proximity thereto;

Fig. 4 is a diagrammatic view showing apparatus for performing the present inven- Fig. 5 is a view, partly in section showing a different form of apparatus adapted to perform the method above described; and,

- Fig. 6 is a view, partly in section, illustrating another form of apparatus for-the same pur ose.

inclusive comprises a conduitadapted to re-' ceive a continuouslyflowing samplev of the mixture of air with a flammablegas or gases,

with means for maintaining the mixture at a higher temperature than the temperature of condensation of the-flammable material,.

with means in the path of the flowing current of mixture to cause combustion, and. means for measuring the increase in temperature causedby such combustion.

In this apparatus the conduit. 1 which, as illustrated in Fig. 4, communicates with the interior of a drying or other chamber 2 containing a mixture of air and inflammable vapor and/or gases, leads to a flashback preventer 3 in the form of a cylindrical ehamber containing a closely wound spiral coil of wire mesh 4 through which the flowing sample of air passes, thence through a continuation 5 of the conduit 1 provided with a regulating valve 6 to the chamber 7 of the testing device. The particular form of testing device illustrated in Figs. 1 to 4 mclusive comprises duplicate casing members 8 and 9, preferably of circular form, having peripheral inwardly extending flanges which are clamped together by a series of bolts 10. A pair of insulating disks 11 and 12, preferably of mica, which are separated from each other and from the flanges of the casing by asbestos packing 13, are clamped between the peripheries of the casing members 8 and 9. The mica disks-11 and 12 are provided with central apertures 14 through which the mixture is caused to flow. A heating unit 15, which may be in the form of a grid of nichrome wire, is located transversely of this aperture and preferably in contact wlth a suitable catalyst 16, such as platinized asbestos. V

The presence of a heating unit may not Be necessary if a suitable catalyst is employed.

Furthermore, a-suitable inert material may be used in place of the catalyst where a heating unit is employed for raising the temperature of the mixture to 'or above' the flamnmabletemperature of the hydrocarbon there- 0 Any suitable means may be employed for measuring the rise in temperature caused by the combustion of the hydrocarbon content of the mixture. As illustrated in Fig. 1 the thermocouple 17 is located in contact with the catalyst or inert material, or in such close proximity thereto as to be in the field of combustion and suitable means are provided for measuring the increase in voltage caused by such combustion.

Preferably the temperature-measuring de vice comprises a hot and a cold thermocouple arranged in series with a millivoltmeter in circuit operable by the differential in voltage produced by the hot and cold thermocouples. As illustrated in Figs. 1 to 4 of the T e apparatus illustrated in Figs. 1 to14- rawings the hot thermocouple 17 is located in contact with, or in close proximity to, the

catalyst within the chamber 7 of the testing wire 20 of chromel connected together to form the hot thermocouple 17, the wire 20 being also connected to a wire of chromel 21 to form the .cold thermocouple 18 with a millitemperature caused by the combustion ofthe flammable content of the mixture being tested, an increase in voltage is produced in the thermocouple 17 which throws the thermocouple system out of balance and causes the ntillivoltmeter to indicate by the movement of its hand 23 the change in voltage due to the differential of the voltages produced by the hot and cold thermocouples. This change in voltage has been found to be in proportion to the content of flammable'material in the mixture so that the scale 24, over which the hand of the voltmeter passes, may be graduat'ed to indicate the proportions of hydrocarbon or other flammable gases in the mixture as well as the changeinvoltage in the differential of the currents produced by the thermocouples. The scale may, if desired, be graduated to indicate arbitrary factors,

such as, explosive limit, dan er, etc.

Any suitable means may e employed for producing the desired continuous flow of the apparatus above described. Desirably, howhydrocarbon-containing mixture through the ever, suitable means for producing a suction 'to draw the mixture through the conduit is mechanism, which is illustrated in the present construction, comprises a combined heater and flashback preventer. The flashback preventer 3, has heretofore been described as comprising a closely coiled body of wire mesh 4 located within the enlarged cylindrical chamber forming part of the conduit through which a sample of the mixture is caused to flow. The means for heating the mixture illustrated herein comprises a heating coil 25 surrounding the cylindrical conduit containing the wire mesh coil and preferably enclosed by a suitable layer of insulating material, such as asbestos composition. The section of conduit 5, containing the regulating valve 6 and leading from this chamber, desirably is as short as may be in order to prevent condensation of the flammable content of the mixture before the mixture comes in contact with the catalyst or other means for causing combustion thereof. ,By suitable manipulation of the regulating valve 6 any desired rate of flow of the mixture throu h the chamber 7 containing the catalyst may e attained.

The use of the invention for continuously testingthe condition of a mixture of air with flammable gases or vapors, and for automatically maintaining the proportion of vapor in the mixture well below thelower explosive limit, is illustrated in Fig. 4 of the drawings in which a chamber 2, such as a' drying chamber, is illustrated as being provided with an inlet 26 for the air and an outlet 27 through which the mixture is drawn by a suitable suction device, such as a fan or pump 28. Any suitable means may be providedfor drawing asample of the mixture of air and hydrocarbon from the drying chamber through the testing device, such, for example, as an electrically driven pump 29 having its intake pipe connectedtto the outlet ofthe testing device.

Means are provided for automatically regulating the rate at which the mixture is drawn from the chamber under the control of the testing and indicating device heretofore described. In the illustrative embodiment of the invention shown in the drawings the outlet pipe 27 is provided with a damper 30which is controlled by a solenoid 31 the energization of which is regulated by the testing mechanism. In the construction illustrated a suitable source of electric power, such as a generator 32, may be employed to furnish the current for the testing apparatus and also for actuating the solenoid. As illustrated herein a conductor 33 leads from the enerator to the heatin coil 25 of the flashiack preventer and om such coil through a conductor 34 to the heating unit 15 of the testing device. From the heating unit a return conductor 35 leads to the other pole of the generator. Another circuit leads from the generator through the conductors 33 and 36 through a switch 37 to the solenoid 31 from which a return conductor 38 extends to the generator 32. The switch 37 normally is maintained in 0 en condition but is ada ted to be closed t rough suitable relays y the action of a testing device when the flammable vapors or gases in the mixture reach or exceed a predetermined proportion. Inasmuch as a very small current is generated bythe thermocouples it is usually necessary to provide one or more relays for actuating the switch 37. As illustrated in the accompanying drawings the circuit of the current produced by the thermocouples through the elements 19, 20 and 21 thereof, includes a solenoid 39 adapted to control a switch 40 in a shunt circuit for operating the switch 37.'

This shunt circuit as illustrated herein comprises a conductor 41 leading from the conductor 33 to'the solenoid 42 of the switch 37 and therefrom to the relay switch 40 which normally is maintained in open condition. A return conductor 43 leads to the return conductor 35 of the circuit which includes the heating units of the'testing device.

In the normal operation of the device illus- 'trated the damper 30 is set to provide for the passage of a certain current of air through the drying chamber sufliciently to maintain a predetermined low proportion of flammable vapors or gases in the mixture produced in. the oven by the vaporization of liquid solvent from the surface of the article placed in the oven. If the vapor content of the mixture in the oven increases above the predetermined amount the increase in temperature in the chamber 7 of the combustion device, which is caused by the combustion of the increased amount of vapor or gas, will produce an increase in voltage in the ther mocouple' circuit, thereby both indicating such increase u on the millivoltmeter, and also actuating t e solenoid 39 to close the shunt circuit through the conductors 41, the switch 40, and return conductors 43 and 35. The current thereupon flowing through this shunt circuit will close the switch 37 thereby completing the circuit from the generator through the solenoid. The actuation of the solenoid 31 wi1l produce an opening movement of the damper 30 thereby enabling the fan to draw the mixture from the oven at an increased rate so that the additional amount that of flammable va ors or gases contained in the mixture. en the additional air thus introduced into the oven has reducedthe proportion of flammable gases or vapors to or below the predetermined amount the reduction of the combustion in the testing device will correspondingly reduce the current produced by the thermocouples and will permit the springs of the relays and switches to break the shunt and solenoid-actuating :circuits respectively so that the damper, which desirably is spring actuated, will be known means may be employed for regulatin the speed of an exhaust fan and other wel known mechanisms and expedients may also be employed for the same purpose.

v It will also be understood that the testing devicemay be arranged to communicate witli any portion of the chamber and also that the device is equally applicable to the testing and regulation of the mixture contained in any part of a continuous conveyer oven or passage through which mixtures containing the flammable material flow. I

It will also be understood that other forms of testing devices may be employed. In Fig. 5 a simplified form of testing device is illustrated which comprises a conduit 44 through which the mixture of air or oxygen with flammable gases is caused to flow with a suitable catalyst 45 located within the condult. The conduit may be surrounded by an electric heating unit 46, or subjected to other means for raising the temperature of the mixture sufliciently to cause iginition of the flammable gases. A hot thermocouple 47 is located preferably within the material of the catalyst,

. with the conductors 48 and 49 leading from said thermocouple to the millivoltme'ter 50. In this device, as in the one previously described, it is desirable that a cold thermo-' couple 51 may be employed in series in the circuit so that the voltmeter will be actuated by the difierential of the currents produced by the respective thermocouples.

Another embodiment of the invention is illustrated in\Fig. 6 which shows a conduit or tube 52 through which the mixture of airor oxygen and flammable gases or vapors iscaused to How continuously with a catalyst 53' located in the tube. In this construction the tube is provided with preferably quartz glass windows 54 and 55- located 'upon opposite sides of the catalyst 53, with plates preferably provided with smooth heat radiating surfaces superposed over the respective windows. These windows permit the heat radiating from the mixture before and after'its contact with the catalyst to pass through them respectively. The indicating device comprises a U-shaped capillary tube 56 containing a liquid 57 in the looped portions thereof- The legs 58 and 59 terminate in enlarged closed chambers 60 and 61 located in proximity to the respective'windows54 and 55 in the conduit 52. The upper walls 62 and 63 of the chambers 60 and 61 respectively are coated with platinum black,'or other heat absorbing material. When the temperature of the vapor upon both sides of the catal st 53' is the same as when no combustion ta es place in the tube, and the liquid 57 in the legs of the tube will remain at the same level in both legs 58 and 59. If,'however, any

proportion of flammable gas ispresent in the air flowing through the conduit 52 the com- 'bustion caused by its contact with the catal st 53 will cause an increase in the heat to which the heat-absorbing top 63 of the chamber 61 is subjected, thereby causing a greater expansion of the gaseous content of this chamber than that of the chamber 60, so that the level of the liquid 57 in the tube 59 will be lowered, while the level of the liquid in the conduit 58 will be correspondingly raised. By providing an electric conductor 64 terminating in the liquid 57 in the tube and an-" other electric conductor 65 leading into the leg 58 of the tube at a suitable distance above the normal level of the liquid 57 the dev ce may be utilized as-a regulating means since the, conductors 64 and 65 may be connected in the circuit of a suitable regulating devlce such as that above described... In such case the capillary tube will constitute a switch temperature caused by the combustion of the vapor content would cause the liquid 57 to rise in the tube 58 until such liquid would complete the circuit through the conductors 64 and 65 and thereupon .the mechanism for controlling the amount of air supplied to the mixture will be actuated.

It will be readily understood that the method and apparatus herein described may be employed not only for determining the proportions of flammable. gases in the mixture with air or oxygen where such propor tions are below the theoretical chemical combimng proportions, but may be employed to determine higher proportions by the dilution of a sample of the mixture .with a known amount of air or oxygen.

It may also be stated that where the proportion of hydrocarbon in the air is known the method may be emplo ed to determine, from the temperature pro uced by combustion in the testing device, the character of the gaseous hydrocarbon contained in the mixture, as the combustion of such gases at the same predetermined roportions produces different amounts of cat units as has heretofore been pointed out.

Having thus described the invention, what is claimed as new, and desired to be secured by Letters Patent, is: I v

1. A universal method of testing the flammable conditions of a mixture of any of the flammable hydrocarbon gases with oxygen containing gases which comprises continu-- from the mlxture asample ously drawin thereof, causmg continuous combustion of the said sample of the mixture, and causlng the increase in tem rature produced by such combustion continuously to indicate the fractional roportion of the amount of heat produced y such combustion relativelyto the constant amount of heat produce by continuous combustion of any hydrocarbon gases at the lower limit of e losive strength of any of the said hydrocar n gases with air.

2. A universal method of testing the flammable conditions of a mixture of any of the flammable hydrocarbon gases with oxygen containing gases which comprises continuously drawing from the mixture a samplegases at the lower limit of explosive strength of any of the said hydrocarbon gases with air. a

3. A universal method of testing the flam mable conditions of a mixture of any of the flammable hydrocarbon gases with oxygen containing gases which comprises continuously drawing from the mixture a sample thereof, causing continuous combustion of the said sample of the mixture and causing the increase in temperature produced by such combustion continuously to produce an electric current havinga voltage propor-- tional to the increase in temperature caused by such combustion and causing the electric current so'produced to indicate the fractional proportion of the amount of heat produced by such combustion relatively to the constant amount of heat produced by continuous combustion of any hydrocarbon gases at the lower limit of e losive st of anyof the said hydrocar n gases with air. Y

4. A universal method of testing the flammable conditions of a mixture of any of the flammable hydrocarbon gases with oxygen containing gases which comprises continuously drawing from the mixture a sample thereof causing continuous combustion of the said the increase in temperature produced by such combustion continuously to produce an electric current having a voltage proportional to the increase in temperature caused A by suchcombustion and causing the electric sample of the mixture and causing current so produced to vary the proportion v of flammable gases in said m1 The method of testing the condition of a mixture of hydrocarbon 's with air contained in a chamber w ch comprises subjecting a continuously flowing sample of the mixture taken from said' chamber to artificial heat to'maintain the same at a temperature sufliciently high to prevent condensation, causing combustion, of said heat d mixture in the presence of a catalyst, electrically measuring the increase in tempera- Y ture caused by said combustion, and causing the increase in such temperature to indicate the proportion of flammable vapors in the mixture relative to the lower limit of explosive stren h thereof.

' 6. The met 0d of testingthe condition of a mixture of hydrocarbon gases with air contained in a chamber which comprises sub-" jecting a. continuously. flowing sam 1e of the mixture taken from said cham r to artificial heat to maintain the same at a temperature suificiently high to; prevent con-- densation, causing combustion ofsaid heated mixture in the presence of a catalyst, preventing flashback into the chamber, electrically measuring the increase in temperature caused by said combustion, and causing the mcrease in such temperature to indicate the proportion of flammable vapors in the mixturerelative to the lower limit of explosive strength thereof.

7. The method of testing the condition of a of hydrocarbon with air contained in a chamber which comprises subjecting a continuously flowing sample of the mixture takenfrom said chamber to artificial'he'at to maintain the same at a temperature sufliciently high to prevent condensatlon, causing combustion of said heated mixture in the presence. of a'eatalyst, causing the increase in temperature produced by such combustiouto produce electric current having a voltage proportional to the increase in temperature caused by such combustion, and causing the variations in the iao e lectri c c u rrent So tova ry the upply of air co-the chamber as to maintain a mixture in -said Chamber well belbw the' lower limitof' explosive strength therebff a Intestimony whereof, I have signed-my name to this specification.

NORMANI J.-,TP1OMPSON; 

